In a Web server by IBM Corporation (Websphere Application Server, hereinafter referred to as an “IBM Web server”), a database, JMS (JavaÒ Message Service) server is defined as an external storage unit to provide data of HTTP session with permanence, and session data is read out through a session data cache prepared for each Web application. To enhance the performance of server, it is required to set the size of the session data cache for each Web application appropriately, but the optimal size is different with an arrival pattern of HTTP request for the Web application. Thus, it is desired that employing a statistical quantity (PMI Data Counter) regarding the performance held by the IBM Web server, the cache hit ratio is estimated when the cache size is changed, and the appropriate cache size is obtained. However, there is a locality in the reference or update pattern of HTTP session data, and if the statistical quantity of PMI (Performance Measurement infrastructure) data counter (PMI Data Counter) is directly employed, the actual hit ratio is undervalued, resulting in a problem of incorrect evaluation.
There is a long history of researching the method of evaluating the hit ratio of cache, in which various methods are provided from analytical to simulation method. An input arrival pattern is generated according to independent probability or a distribution in dependent relation to deal with the locality. However, the hit ratio in an actual system is evaluated or analyzed posteriori by acquiring detailed data. In the server system and the like, where it is practically impossible to acquire detailed data during actual operation due to overhead, those methods are difficult to apply.
A device of patent document 1 is concerned with a cache interposed between CPU and main storage but not the cache of server. In a computer of patent document 1, the cache system option (direct map/set associative) and the cache line size are settable to enable the application itself to maximize the hit ratio so that an application may know the hit ratio during execution of a job.
A device of patent document 2 is concerned with a cache of server, in which the empirical expression f(x) regarding the occurrence number includes a predetermined feature parameter, the size and entry number of session data actually employed in the total size of cache are recorded at regular intervals, the occurrence order x and the occurrence number f(x) corresponding to x are obtained based on the recorded data, the predetermined feature parameter is detected based on the obtained value of f(x), the cache hit ratio and the entry number S are estimated from the feature parameter, and an appropriate cache size is calculated based on the estimated cache hit ratio and entry number S.
A device of patent document 3 does not involve the cache of the server but involves the cache interposed between CPU and main storage. In the device of patent document 3, the block size of cache is virtually changed during execution of application, to calculate the hit number, and decide the size of data transfer based on the hit number, thereby improving the hit ratio of cache.
A device of patent document 4 does not involve the cache of the server but involves the cache interposed between CPU and main storage. In the patent document 4, it is disclosed that the total execution clock number for a program of evaluation object is obtained in consideration of the cache hit ratio.
Patent Document 1
Published Unexamined Patent Application No. 5-225060
Patent Document 2
Published Unexamined Patent Application No. 2000-155713
Patent Document 3
Published Unexamined Patent Application No. 2000-250809
Patent Document 4
Published Unexamined Patent Application No. 10-133902